Re: [PATCH v2] ACPI: video: Fix random crashes due to bad kfree

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11-Jan-25 7:59 PM, Chris Bainbridge wrote:
> Commit c6a837088bed ("drm/amd/display: Fetch the EDID from _DDC if
> available for eDP") added function dm_helpers_probe_acpi_edid, which
> fetches the EDID from the BIOS by calling acpi_video_get_edid.
> acpi_video_get_edid returns a pointer to the EDID, but this pointer does
> not originate from kmalloc - it is actually the internal "pointer" field
> from an acpi_buffer struct (which did come from kmalloc).
> dm_helpers_probe_acpi_edid then attempts to kfree the EDID pointer,
> resulting in memory corruption which leads to random, intermittent
> crashes (e.g. 4% of boots will fail with some Oops).
> 
> Fix this by allocating a new array (which can be safely freed) for the
> EDID data, and correctly freeing the acpi_buffer pointer.
> 
> The only other caller of acpi_video_get_edid is nouveau_acpi_edid:
> remove the extraneous kmemdup here as the EDID data is now copied in
> acpi_video_device_EDID.
> 
> Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
> Fixes: c6a837088bed ("drm/amd/display: Fetch the EDID from _DDC if available for eDP")
> ---> Changes in v2:
> 	- check kmemdup() return value
> 	- move buffer management into acpi_video_device_EDID()
> 	- return actual length value of buffer

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Regards,

Hans



> ---
>  drivers/acpi/acpi_video.c              | 50 ++++++++++++++------------
>  drivers/gpu/drm/nouveau/nouveau_acpi.c |  2 +-
>  2 files changed, 29 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index 8274a17872ed..3c627bdf2d1b 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -610,16 +610,29 @@ acpi_video_device_lcd_get_level_current(struct acpi_video_device *device,
>  	return 0;
>  }
>  
> +/*
> + *  Arg:
> + *	device	: video output device (LCD, CRT, ..)
> + *	edid    : address for returned EDID pointer
> + *	length  : _DDC length to request (must be a multiple of 128)
> + *
> + *  Return Value:
> + *	Length of EDID (positive value) or error (negative value)
> + *
> + *  Get EDID from ACPI _DDC. On success, a pointer to the EDID data is written
> + *  to the edid address, and the length of the EDID is returned. The caller is
> + *  responsible for freeing the edid pointer.
> + */
> +
>  static int
> -acpi_video_device_EDID(struct acpi_video_device *device,
> -		       union acpi_object **edid, int length)
> +acpi_video_device_EDID(struct acpi_video_device *device, void **edid, int length)
>  {
> -	int status;
> +	acpi_status status;
>  	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
>  	union acpi_object *obj;
>  	union acpi_object arg0 = { ACPI_TYPE_INTEGER };
>  	struct acpi_object_list args = { 1, &arg0 };
> -
> +	int ret;
>  
>  	*edid = NULL;
>  
> @@ -636,16 +649,17 @@ acpi_video_device_EDID(struct acpi_video_device *device,
>  
>  	obj = buffer.pointer;
>  
> -	if (obj && obj->type == ACPI_TYPE_BUFFER)
> -		*edid = obj;
> -	else {
> +	if (obj && obj->type == ACPI_TYPE_BUFFER) {
> +		*edid = kmemdup(obj->buffer.pointer, obj->buffer.length, GFP_KERNEL);
> +		ret = *edid ? obj->buffer.length : -ENOMEM;
> +	} else {
>  		acpi_handle_debug(device->dev->handle,
>  				 "Invalid _DDC data for length %d\n", length);
> -		status = -EFAULT;
> -		kfree(obj);
> +		ret = -EFAULT;
>  	}
>  
> -	return status;
> +	kfree(obj);
> +	return ret;
>  }
>  
>  /* bus */
> @@ -1435,9 +1449,7 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
>  {
>  	struct acpi_video_bus *video;
>  	struct acpi_video_device *video_device;
> -	union acpi_object *buffer = NULL;
> -	acpi_status status;
> -	int i, length;
> +	int i, length, ret;
>  
>  	if (!device || !acpi_driver_data(device))
>  		return -EINVAL;
> @@ -1477,16 +1489,10 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
>  		}
>  
>  		for (length = 512; length > 0; length -= 128) {
> -			status = acpi_video_device_EDID(video_device, &buffer,
> -							length);
> -			if (ACPI_SUCCESS(status))
> -				break;
> +			ret = acpi_video_device_EDID(video_device, edid, length);
> +			if (ret > 0)
> +				return ret;
>  		}
> -		if (!length)
> -			continue;
> -
> -		*edid = buffer->buffer.pointer;
> -		return length;
>  	}
>  
>  	return -ENODEV;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> index 8f0c69aad248..21b56cc7605c 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> @@ -384,7 +384,7 @@ nouveau_acpi_edid(struct drm_device *dev, struct drm_connector *connector)
>  	if (ret < 0)
>  		return NULL;
>  
> -	return kmemdup(edid, EDID_LENGTH, GFP_KERNEL);
> +	return edid;
>  }
>  
>  bool nouveau_acpi_video_backlight_use_native(void)